Air hardening cast iron



June 25, 1963 w. H. MOORE `L-:TAL

AIR HARDENING CAST IRON Filed Feb. 24, 1961 2 Sheets-Sheet l R R www No mow we NM@ uw HE M mm. ,W LU L Mm Y m B U June 25, 1963 w. H. MOORE ETAL AIR HARDENING CAST IRON 2 Sheets-Sheet 2 Filed Feb. 24, 1961 /N VEN TORS W/l. L /AM H MOORE WALTER E @Rl/VER JR.

United States Patent O 3,095,300 AIR HARDENING CAST IRON William H. Moore and Walter E. Gruver, Jr., New Rochelle, NX., assignors to Meehanite Metal Corporation, a corporation of Missouri Filed Feb. 24, 1961, Ser. No. 91,468 3 Claims. (Cl. 75-123) The present invention relates to -a unique gray cast iron having an improved and unusual combination of properties, particularly in that it is readily machinable in the ascast condition and may be hardened without distortion, to provide improved Wear resist-ance, hardness and strength.

In the held of engineering cast iron castings, it is common practice .to harden the casting after the machining operation for the purpose of providing a higher hardness. This hardening may be local, :as in llame or induction hardening, or i-t may be overall, as in quenching in oil or water or air. Local hardening -becomes increasingly complex as the part itself becomes complex, and at the best, is only a skin effect, seldom being more than l/s deep. Conventional hardening in quenching medium such as oil or water, is quite drastic and leads to the development of severe stresses in the part. These stresses may cause dimensional changes and even cracking of the castings. Hardening in -air is less severe `and causes very little dimensionalichange, however, for a cast iron to be air-hardenable, it has to have an alloy content that will confer upon it the necesary hardenability.

The present invention is based on the discovery that the combina-tion of manganese and molybdenum in a cast iron composition will confer this air-hardening ability to a pronounced degree.

It is an object of this invention -to provide a cast iron of novel composition, which is machinable afs-cast andv which can be hardened in air.

it is a further object of this invention .to provide a cast iron of unusual properties when it has been hardened in air.

IIt is la further object to provide a cast iron which can be hardened in `air with little or no dimensional distortion or danger of cracking.

Other objects and advantages of the present invention will be apparent to those skilled in the -art from the following description, taken in conjunction with the drawings in which:

FIGURE 1 is a drawing showing the preferred composition ranges for the alloy of this invention;

FIGURE 2 is a reproduction of a photomicrograph taken at 750 diameters and showing the etched structure in the ias-cast condition of an alloy produced in accordance with the present invention; and

FIGURE 3 is a reproduction of a photomicrograph taken at 750 diameters and showing the etched structure in the air hardened condition of an alloy produced in accordance with the present invention.

The present invention provides a novel ferrous product containing at least about 50% iron, carbon and silicon Within the cast iron range and manganese ranging from 1.2 to 5.3% and molybdenum ranging irom 0.40% to 0.80%, with the product being substantially pearlitic in the `as-cast condition and substantially acicular or martensitic in the air hardened condition. By air hardening is meant heating a casting to within the critical range, where the casting is Wholly -austenitic, andthen cooling rapidly in still or moving air.

The use of manganese :and molybdenum in combination as :alloyisng elements in cast iron is old in the art. Also, the use of other alloying combinations, notably nickel and molybdenum, to produce a `cast iron which can be air hardened, is old in the art. It has been found, however, that when the combination of manganese and molyb- 3,095,300 Patented June 25, 1963 Mnce 2 denum is kept in the range illustrated in FIGURE 1, and this iron is subsequently air hardened, it produces proper- Ities in the iron which are quite diiierent from those obtainedl with other alloy combinations.

Dealing speciiically with FIGURE 1, it has been found that the alloy of this invention must ibe kept substantially within fthe range marked Correct composition Range.

If the alloy vcomposition for any given section falls above the upper line AA of this range, it will contain some martensite or acicular components in the ias-cast condi- :tion and will be diicult .to machine, unless it is given a prolonged and costly annealing treatment. If, on the other hand, the alloy `composition iior any given section falls below the lower line BB it will be incapable of being converted to the fully acicular or martensitic condition by an air hardening heat treatment.

The presence of other elements in the composition in more than trace amounts such as nickel, tungsten, chrormium, cobalt, copper, and vanadium, will also slightly aiiect the relative positions of the lines AA and BB, but will in no way detract from the qualities of the cast iron of the invention, providing the essential elements manganese and molybdenum are present in the ranges quoted.

The unusual characteristics of the alloy oi? this invention 'are best illustrated by a series of examples:

In the iirst example, a bar, having Ia 2 diameter was cast from la melt of the following composition.

Iron A: Percent Total carbon 3.20 Silicon 1.70 Manganese 2.0 Molybdenum .70

For purposes of comparison another bar of the same diameter was cast from Ia melt of the following composition.

Both these bars were allowed [to cool slowly in the mold, and when completely cool they |were removed from the mold and checked for hardness.

These bars were both then heated up to a temperature of 1550 degrees yFahrenheit for a period of 11/2 hours.` They were 'then withdrawn simultaneously from the -furnace and allowed to cool to room temperature in the air. Both bars were again checked for hardness.

They were then sectioned into several pieces and these pieces, one at a time, from each bar, were placed in a furnace and heated to successively higher drawing temperatu-res. The pieces were held 4at eachdrawing temper-ature for la period of one hour and they were then fcooled slowly in the furnace. The hardness of each piece so treated was again measured. The hardness results obtained in this test are ltabulated in v'Table No. 1.

TABLE NO. 1

Brinell Hardness Values of T wo Air Hadenng Cast Irons It should be noted that the alloy of this invention, containing the required manganese and molybdenum content in accordance with `FIGURE 1, is at a much higher value at all drawing temperatures up to 1200 degrees E This means, in effect, that Athe alloy .o-f this composition, when air hardened, is table to maintain a higher working hardness at elevated temperatures than another well known air hardening composition employing nickel and molybdenum as the essential ingredients. As many mod ern industrial engineering parts are expected to perform at temperatures which are higher than room temperature, this means that the Kalloy of this invention will give improved Wear resistance at elevated temperatures. This fact has heen confirmed by actual castings used in industry.

=In another test a melt was made :and cast into a 3" test bar. The `composition of the sample taken from this bar was:

Percent Total carbon 3.10 Silicon 1.85 Molybdenum .65 Manganese 2.51

In the las-cast condition this bar was found to have a Brinell hardness of 241. yIt was readily machinable and a test @bar was machined from a portion of Vthis bar and tested for tensile strength. The tensile strength obtained was 44,500 p.s.i. The remaining portion of this bar was then heated to a temperature of 1600 degrees F., held there for two hours and removed from the furnace and cooled in moving air by means of `a small fan. This bar was then :returned to another furnace and drawn at a temperature of 500 degrees -F A test bar was cut from this soI treated portion of the bar and was found to have a tensile strength of 72,500 p.s.i. with a Brinell hardness of 466. This test clearly illustrates the combination of high h-ardness and high strength that is Iavailable with the alloy of this invention.

In the third example a melt was produced and cast in a bar having a casting section. This melt had the following composition:

Percent Total carbon 3.05 Silicon 1.90 Molybdenum 0.72 Manganese 4.95

The hardness of this har in the as-cast condition was 228 and the structure consisted essentially of pearlite with excess graphite in the ilake form. This bar was then heated in the furnace to a temperature `of 1550 degrees F., held for four hours, removed from the furnace and cooled in the air. The hardness was found to be 466 Brinell and the structure was essentially acicular in nature.

A portion of this `bar was then hammered severely on the surface, so that deformation occurred. The hardness in this deformed area was .found to have increased the hardness to 555.

rIlhis test serves to illustrate the work hardening propensity obtained by the alloy -of this invention. This is a useful characteristic in the manufacture of castings which are to be subjected to abrasive wear.

`In a further test, a sleeve casting was made having an as-cast section of 11/2" from a melt falling within the composition limits shown in FIGURE 1. This sleeve was fully machined and was found to have a 6.000 inch diameter along its full length of 12". The hardness in the asmachined condition was found to be 217 Brinell. This sleeve casting was then piaced in a furnace, heated to 1600 degrees F., removed from the furnace and .air cooled. The hardness in the air cooled condition was found to be 555 Brinell. The dimensions of the liner -Were measured along its ful-l length and was found to range `from 5.999 inches to 6.001 inches. This is considered a relatively i small amount of distortion and castings of the same type made from ordinary cast iron which has been hardened by quenching in oil usually show a dimensional variance of more than .005.

This illustrates the ability lof the alloy of this invention to be air hardened with very little distortion.

it has been found that the alloy of this invention may readily be :treated with certain suitable nodularizing agents, so that the free graphite occurs in the nodular of spheroidal form. Such treatment increases the strength obtained without in any way interfering with the hardness values obtained vor with the other important characteristics of the alloy. It has been found also, that the Ialloy of the composition indicated in FIGURE 1 has no adverse effect on conventional methods of producing the nodular form of graphite.

Although -the present invention has been described in conjunction with preferred interpretations, it is to be understood that modifications and variations may be resorted to Without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such variations and modifications, apparent to Ithose skilled in the art, yare considered to be within the purview and scope of the invention and the intended claims.

What is claimed is:

1. A gray iron casting having la definite manganese content in relation to the cross section thereof, said casting, in percent yby weight, consisting essentially of total carbon in the range of from 2.80% to 3.30%, silicon in the range of 1.60% to 2.20%, molybdenum in the range of from .40% to .80%, manganese in the range of from 1.2% to 5.3%, and the balance essentially iron, the manganese content and the cross section `of the casting being further limited in amount and cross section to an intersection of the ordinate and abscissa within the area defined by lines AA 'and BB vof FIGURE 1 of the drawing.

2. A gray iron casting having excess carbon in the form of flakes or nodules and having a definite manganese content in relation to the cross section thereof, said casting, in percent by weight, consisting essentially of total carbon in the range of from 2.80% to 3.30%, silicon in the range of 1.60% Ito 2.20%, molybdenum in the range of from .40% -to .80%, manganese in the range of from 1.2% to 5.3%, and the balance essentially iron, the manganese content and the cross section of the casting being further limited in amount and cross section -to an intersection of the ordinate and abscissa within the area defined by lines AA land BB of FIGURE 1 of the drawing, said casting being further characterized by having an as cast matrix of pearlite and an air hardened matrix of martensite.

3. A gray iron casting having excess carbon in the form of flakes or nodules and having a definite manganese content in relation 4to the cross section thereof, said casting, consisting essentially of carbon 'and silicon in the gray cast iron range, molybdenum in the range of from .40% to .80% by weight, manganese in the range of from 1.2% to 5.3% by Weight, and the balance essentially iron, the manganese content and the cross section of the casting being further limited in 4amount and cross section to an intersection of the ordinate and abscissa within the area defined by lines AA and BB of FIGURE l of the drawing, said casting being further characterized by having an as cast matrix of pearlite and an air hardened matrix of martensite.

References Cited in the file of this patent UNITED STATES PATENTS 2,105,220 Lauenstein Jan. '11, 193s FOREIGN PATENTS 479,584 Great Britain `Feb. 8, 1938 

1. A GRAY IRON CASTING HAVING A DEFINITE MANGANESE CONTENT IN RELATION TO THE CROSS SECTION THEREOF, SAID CASTING, IN PERCENT BY WEIGHT, CONSISTING ESSENTIALLY OF TOTAL CARBON IN THE RANGE OF FROM 2.80% TO 3.30%, SILICON IN THE RANGE OF 1.6% TO 2.20%, MOLYBDENUM IN THE RANGE OF FROM .40% TO .80%, MANGANESE IN THE RANGE OF FROM 1.2% TO 5.3%, AND THE BALANCE ESSENTIALLY IRON, THE MANGANESE CONTENT AND THE CROSS SECTION OF THE CASTING BEING FURTHER LIMITED IN AMOUNT AND CROSS SECTION TO AN INTERSECTION OF THE ORDINATE AND ABSCISSA WITHIN THE AREA DEFINED BY LINES AA AND BB OF FIGURE 1 OF THE DRAWING. 